A polycarbonate resin is excellent in the mechanical strength, electrical properties, transparency, etc. and is widely utilized as an engineering plastic in various fields such as electric/electronic device field and automotive field. Recently, in these application fields, reduction in the thickness, size and weight of a molded/processed product has progressed, and the performance of a molding material is required to be more enhanced. Among these, development of a polycarbonate resin having high flame retardancy even with a small thickness is desired, and several proposals have been made thereon.
For example, a method for making a polycarbonate or copolycarbonate having an excellent surface hardness by using bisphenols different from the conventional bisphenol A (Patent Document 1 or 2), and a method for balancing flowability and hardness by blending a dimethyl bisphenol cyclohexane-type polycarbonate and a bisphenol A-type polycarbonate (Patent Document 3), are known.
On the other hand, in Patent Document 4, a technique of incorporating a branching agent (a monomer having three or more reactive groups; a unit capable of becoming a repeating unit) and thereby partially introducing a branch structure so as to enhance the flame retardancy is known. However, introduction of a branching agent makes it difficult to control the extent of crosslinking produced at the time of polymerization of a polymer, and there is a problem that a gel-like substance is produced and causes a foreign matter.